Photophysics of Ion Clusters Formed between [Ru(bpy)3]2+ and the Polyoxotungstate Anion [S2W18O62]4-

The interactions between [Ru(bpy) 3 ] 2+ and the polyoxotungstate anion [S 2 W 18 O 62 ] 4- in acetonitrile solution were investigated using a combination of photophysics and optical and Raman spectroscopies. The presence of ion clusters of {[Ru(bpy) 3 ][S 2 W 18 O 62 ]} 2- ( K 2 = 7.7 × 10 5 ) and [Ru(bpy) 3 ] 2 [S 2 W 18 O 62 ] ( K 1 = 1.0 × 10 6 mol -2 dm -6 ) are inferred. The 2:1 complex is weakly luminescent, with a lifetime at room temperature of 20 ns under aerobic conditions. Difference electronic absorption, excitation, and resonance Raman spectroscopies indicate that the tungstate anion participates in this transition. Under conditions where [Ru(bpy) 3 ] 2+ alone is photolabile, the ion clusters are photostable, with no photodecomposition or photoinduced ligand exchange reactions evident in acetonitrile. This characteristic is examined employing temperature-dependent luminescent studies which demonstrate that the observed activation energy and preexponential factor are considerably different from those of free [Ru(bpy) 3 ] 2+ and are characteristic of a photostable polypyridylruthenium complex.